The present invention relates to a low cost electric system composed of a new DC brushless permanent magnet motor and its electronic drive which provides high efficiency operation and low torque ripple for the motorization of electric vehicles like, bicycles, rolling chairs, scooters, tricycles, golf cars, trolleys and small utility vehicles.
The motor and its electronic system are supplied by one or several batteries. The vehicle wheel drive can be direct to maximize efficiency or equipped with a speed reducer to minimize the motor size. The proposed solution uses a permanent magnet three-phase motor which can reach four times the nominal torque. This motor structure includes an outer rotor which can be fitted into a vehicle wheel. It can be used as motor or generator with energy recuperation in the battery during braking periods or to create electricity to recharge battery, or power other devices by changing the motor. This motor structure is supplied by a PWM (Pulse Width Modulation) current controlled inverter. The operator can impose the machine torque level in motor or generator operation by setting a current reference. The shape of the alternative phase current waveform is rectangular with a width of 120 electrical degrees. This kind of motor supply is the simplest to realize and it reduces the cost of the control system and the number of sensors.
The brushless motor includes a cylindrical outer rotor wherein permanent magnets are mounted on the surface and an internal stator with coils of insulated wire wound around the teeth. There are twenty two magnet poles on the rotor alternatively magnetized north and south and twenty-four slots on the stator. This combination of slots and poles for a three-phase motor structure allows the realization of a special concentrated winding around the teeth with only one coil per slot. In this case, there are only twelve coils to realize. The winding coefficient and the copper filling factor are higher than in the other known solutions described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378 which are using winding with two coils per slot.
This kind of winding with one coil per slot simplifies the assembling of the rotor position sensors (i.e. Hall detectors) near the air gap. The Hall detectors are fixed on the side of several teeth which have no winding and they are using the leakage flux of the permanent magnets to detect the rotor position.
The proposed structure maximizes the energy efficiency and the motor starting torque per unit volume of winding. The advantages of a concentrated winding around the teeth in comparison with a classical distributed winding are described in Konecny U.S. Pat. No. 4,774,428 and Permanent magnet Brushless DC motor with soft metal powder for automotive applicationxe2x80x94J. Cros, P. Viarouge IEEE Industry applications Societyxe2x80x94St-Louis, October 1998. [1]. The volume of copper is reduced and subsequently the Joule losses are minimized.
The amount of vibrations and the cogging torque ripple are reduced drastically like in the other structure combinations described by Konecny U.S. Pat. No. 4,774,428, Huang and al. U.S. Pat. No. 5,675,196 and Katsuma and al. U.S. Pat. No. 4,719,378. The least common multiple (LCM) of the motor""s poles and slots describes how many peaks of cogging torque will be present over a single revolution of the motor. In this case, there are 264 torque pulses per revolution and consequently, the cogging torque amplitude is very low (less than 3% of the rated torque).
The proposed motor structure also minimizes the net radial force like another structure described by Huang and al. U.S. Pat. No. 5,675,196.
The electronic supply includes a power electronics system and a control electronics system. Both systems can be inserted inside the motor housing, in the center of the stator yoke. The power electronics system is composed of an inverter with six Mosfets or multiple Mosfets which operate like six Mosfets. The structure diodes of the mosfets are used to ensure the current reversibility. At each sequence of conduction defined by the rotor position detector, two transistors are switched on to supply two motor phases. In the classical mode of operation, a modulation signal is applied on the gate of these two systems. Both systems can be inserted inside the motor housing, in the center of the stator yoke. The power electronics system is composed of an inverter with six Mosfets or multiple Mosfets which operate like six Mosfets. The structure diodes of the mosfets are used to ensure the current reversibility. At each sequence of conduction defined by the rotor position detector, two transistors are switched on to supply two motor phases. In the classical mode of operation, a modulation signal is applied on the gate of these two transistors. This method simplifies the control realization and only one current sensor can be inserted in the DC bus for the current measurement.
Another solution consists in applying the modulation signal on one transistor only at each sequence of operation: this method is a single switch modulation technique. The other transistor is switched xe2x80x9conxe2x80x9d during all the duration of this sequence of conduction. An example of the single switch modulation is described in an article titled E.M.I. tests on a brushless actuator is described in Comparison of M. Lajoie-Mazene, J. P. Berryxe2x80x94European Power Electronicsxe2x80x94Brighton (U. K.), September 1993 (EMI Tests), in the case of motoring operation only, compared to the classical mode of operation where the modulation signal is applied on the gate of the two transistors. It is shown that the single switch modulation provides lower electromagnetic interferences (EMI and reduces the commutation losses, the conduction losses in low voltage applications, the current ripple and the size of the input filtering capacitor. The proposed electronic system is using the single switch modulation and it can be used for motor as well as generator operation. Consequently, the current regulation is realized without any external current sensor.
It is a feature of the present invention to provide a high performance brushless DC permanent magnet motor and a pulse width modulation electronic inverter for the motorization of electric vehicles supplied with electrical batteries. The motor structure includes an outer rotor which can be fitted to a vehicle wheel. It can be used as a motor or as a generator with recuperation of kinetic energy in the batteries during braking periods.
Another feature of the invention is to provide a special design and the design of its three-phase winding maximize the energy efficiency and the motor starting torque per unit volume of winding. A concentrated winding is wound around the teeth with only one coil per slot. This solution simplifies the winding realization and maximizes the winding coefficient and the copper filling factor.
Another feature of the invention is that the assembling of the rotor position sensor (i.e. Hall detectors) near the air gap is simplified by the winding configuration. The Hall detectors are fixed on the side of several teeth which have no winding and they are using the leakage flux of the permanent magnets to detect the rotor position. The amount of vibrations, the cogging torque ripple and the radial force are greatly reduced.
Another feature of the invention is to provide specific inverter control system which reduces the commutation losses, the diode conduction losses in low voltage applications, the current ripple, the size of the input filtering capacitor and electromagnetic interference. A specific single switch modulation technique is used: The modulation signal is applied only on one transistor at each sequence of operation defined by the rotor position detector. The other transistor is switched on during all the duration of this sequence of conduction. This single switch modulation method maximizes the efficiency of the electronic supply and the current regulation is realized without any external current sensor.
According to the above features, from a broad aspect, the present invention provides a brushless DC motor for electrical vehicle motorization. The motor comprises a cylindrical rotor with 22 poles constructed with segments of permanent magnet material alternatively magnetized north and south. A stator core of ferromagnetic material is spaced inwardly of the rotor and defines a magnetic clearance gap therebetween. The stator core has twenty four slots and define teeth between the slots. A three-phase winding with coils of insulated wire is wound around the teeth. There is provided one coil per slot with predetermined connection patterns Axe2x80x2, C, C, Bxe2x80x2, Bxe2x80x2, A, A, Cxe2x80x2, Cxe2x80x2, B, B, and Axe2x80x2 resulting in reduced torque ripple without any slot or magnet skewing.
According to a still further broad aspect of the present invention there is provided a brushless DC motor as above described but wherein there is further provided two coils per slot having predetermined connection patterns Cxe2x80x2, C, Cxe2x80x2, C, B, Bxe2x80x2, B, Bxe2x80x2, Axe2x80x2, A, Axe2x80x2, A, C, Cxe2x80x2, C, Cxe2x80x2, Bxe2x80x2, B, Bxe2x80x2, B, A, Axe2x80x2, A, Axe2x80x2.
According to a still further broad aspect of the present invention there is provided a brushless DC motor electronic pulse with modulation driver and control system. It includes a power electronic three phase inverter having six power of mosfets. A current control system is coupled to the inverter for generating a 120 electrical degrees rectangular phase current pulses. An electronic control system is provided for both motor and a generator operation mode of the motor and uses a single switch modulation technique.
According to a still further broad aspect of the present invention there is provided a brushless DC motor for breaking a wheel of devices on which people are displaced by self-motorization or electric motor motorization. The motor comprises a cylindrical rotor with twenty two poles constructed with segments of permanent magnet material alternatively magnetized north and south, a stator core of ferromagnetic material spaced inwardly of said rotor and defining a magnetic clearance gap, therebetween said stator core having twenty-four slots and defining teeth between said slots, a three phase winding with coils of insulated wire being wound around the teeth. The rotor is connected to a hub of the wheel. Control circuit means is provided to control the torque of the motor and therefore its arresting force.